In agricultural operating implements there is the danger that damage to the drive line or to driven components can occur due to overloads. For example, in the case of balers or towed forage harvesters, a blockage or stoppage of the elements that take up or convey the harvested crop, which in turn can overload the drive line. Other examples are rotating ground breaking implements that become overloaded at excessive operating depths or heavy ground conditions, or mowing implements, that are stalled by excessively heavy plant components. Therefore it is usual practice to provide operating implements with overload clutches that separate the drive line in case a turn-off torque is exceeded. For this purpose reference is made to the state of the art according to DE 295 04 531 U1 and DE 195 38 370 C1.
Furthermore, the towing or carrier vehicle that moves the agricultural implements across the field, typically includes a drive engine, that is connected over a separable power take-off shaft clutch to a power take-off shaft output for the connection to the drive line of the operating implement and is usually equipped with a sensor for the detection of the torque at the output of the power take-off shaft, that is in turn connected to a control arrangement, that disengages the power take-off shaft clutch, in order to prevent damage to the power take-off shaft drive line (see DE 101 45 588 A1). In the case of such arrangements, the cut-off torque may also depend upon the operating implement and its operating condition (DE 34 34 825 A1).
As a rule, the overload clutch of the operating implement shuts off at torques that do not yet lead to a cut-off of the power take-off shaft clutch. The operator of the carrier vehicle or towing vehicle then has no other option than to remove the cause of the overload manually, that is, for example, in the case of a harvesting machine (baler or forage harvester) to climb out of the cab, to remove the obstruction of the elements used to take up or convey away the harvested crop and then to return to the cab, in order to continue the harvesting operation, since the cause of the overload (that is the blockage in the case of the harvesting machine) still exists after re-engaging the power take of shaft clutch again (unless it had been removed previously) and this leads to the fact that the overload clutch continues to be disengaged. The process described here is time consuming, inconvenient and uncomfortable.
To overcome this disadvantage DE 199 32 272 A1 proposes that operating elements of a baler be driven by means of safety clutches whose cut-off torque can be increased by an increase of the operating pressure. If a load peak has been detected by a rotational speed sensor at a safety clutch, its operating pressure is automatically increased briefly to overcome the load peak. If this increase results in a removal of the cause of the load peak, the normal operation is again resumed, on the other hand, the operating pressure of the safety clutch can be increased further and further measures are taken to reduce the cause of the overload such as by increasing the flow capacity of the conveying channels. The disadvantage here is seen in the relatively high cost of the safety clutches with their variable cut-off torque.